#include<stdio.h>
#include<math.h>
double zhouchang(int x1,int y1,int x2,int y2);
double S(double a,double b,double c);


#include<stdio.h>
#include<math.h>
double zhouchang(int x1,int y1,int x2,int y2);
double S(double a,double b,double c);


double zhouchang(int x1,int y1,int x2,int y2);改成
double zhouchang(double x1,double y1,double x2,double y2);